Al Qaeda in Iraq’s campaign of terrorism and intimidation had turned its Sunni base of support against it. The result was the so-called Anbar Awakening in the late summer of 2006, followed by similar awakening movements across Iraq.
From 2003 through 2006, United States military forces, under the leadership of Gen. John Abizaid and Gen. George Casey, inflicted huge losses on the Baathist and Qaeda leadership. Many thousands of insurgents, including the Qaeda chief in Iraq, Abu Musab al-Zarqawi, were captured or killed and proved difficult to replace.